Scientists unearth fossilized, flightless, four-foot terror bird

An exquisitely preserved skeleton unearthed in Argentina reveals clues about how ancient terror birds communicated. 

F.J. Degrange, M. Taglioretti and F. Scaglia
The skull of LLallawavis scagliai, with scale.

The fossil of this prehistoric bird is so complete, paleontologists can tell you how good its hearing was.

The specimen of Llallawavis scagliai, a species of terror bird described for the first time in the current issue of the Journal of Vertebrate Paleontology, is more than 90 percent intact, making it the most complete fossil of its kind. With this new specimen, researchers hope to reach new conclusions about how these fearsome avian predators behaved.

Terror birds, or phorusrhacids, are an extinct family of carnivorous bird native to South America during the Cenozoic period. Swift and flightless, they were the apex predators of their day. Some larger species stood 10-feet tall. L. scagliai, which means “Scaglia’s Magnificent Bird,” stood at about four feet and lived about 3.5 million years ago in what is today Argentina.

In a field where nearly complete specimens are rare, a nearly complete bird fossil is extraordinary. With their light builds and hollow bones, birds are poor candidates for fossil preservation. But the skeleton of L. scagliai, to the continued wonder of researchers, was almost perfectly intact.

“It is quite rare in South America – almost impossible if you think thoroughly,” says lead author Federico Degrange in an email interview with The Christian Science Monitor. “There are few places where delicate bones, such as those of birds, remain as beautifully preserved as Llallawavis.”

Dr. Degrange says this specimen provides a rare opportunity to study the finer anatomic functions of terror birds. The sclerotic rings – extremely fragile bones used by birds and dinosaurs to focus their eyesight by adjusting the shape of the cornea – are almost never preserved. Even more strikingly, L. scagliai’s cartilaginous windpipe ossified, hardening into bone. Throw in a complete auditory region in the skull, and researchers can study how the bird vocalized. Degrange’s team found that Llallawavis would have communicated in low-frequency calls.

Ohio University paleontologist Lawrence Witmer, who specializes in the functional anatomy of extinct animals, has found a similar emphasis on low-frequency sound in Tyrannosaurus rex.

“It looks like Llallawavis emphasized low-frequency hearing, which is an important finding because it provides clues about potential behaviors,” said Dr. Witmer, who was not involved in the study. “Low-frequency sounds are transmitted over long distances with little attenuation, and so it enables long-distance communication as well as the ability to track prey herd movements even when they aren’t in view.”

And with a specimen so complete, there’s plenty left to learn about the feathered terrors of yesteryear.

“Beyond the skull, there are many other potential studies that this unique specimen will enable, such as studies of speed and style of locomotion,” Witmer said. “A specimen this nice really opens a window into the past, giving us a much clearer view of what terror birds were really like.”

A new skeleton may paint a more complete picture of how these beaked predators lived, but it could also change our understanding of how they died.

“We are able to say now that terror birds were more diverse by the late Pliocene than previously thought,” Degrange said. “This gives us the possibility to re-evaluate the hypothesis about the causes of terror bird extinction.”

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